1. Field of the Invention
The present invention relates to permanent magnet generators, and in particular to a multiple winding permanent magnet generator including switching circuitry for selectively coupling the windings of the generator to provide the desired output voltage.
2. Description of the Prior Art
It is well known that the output voltage from a permanent magnet generator is directly proportional to the RPM of the generator drive shaft. Constant output voltages from permanent magnet generators are typically obtained by either closely regulating the RPM of the generator shaft or by providing a specially designed electronic voltage regulator which is capable of operating over wide RPM ranges. This latter type of voltage regulating device is not only expensive but also highly inefficient.
Remotely located diesel driven pumps or electrical generating apparatus are frequently utilized to provide an emergency or stand-by backup feature. These diesel engines are designed to be activated only when needed and rarely have access to a source of electrical power for maintaining a battery in a charged state.
The more modern diesel engines used in these applications incorporate an electronically controlled fuel injection system which must have a voltage source of a predetermined minimum magnitude in order to permit normal operation of the engine. These infrequently operated diesel engines are started by high pressure air starting systems which are capable of rotating the engine at rates of over 100 RPM. It is therefore a requirement that a mechanically rotatable power source be provided for powering at a sufficient level, the diesel engine electronic fuel injection system at an engine RPM of less than the maximum obtainable RPM from the diesel engine pneumatic starting system.
U.S. Pat. No. 3,396,325 (Hopkinson) discloses a permanent magnet generator the output voltage of which is controlled by a special control winding which requires a low power external power supply for proper operation. U.S. Pat. No. 3,401,290 (Potter) discloses a permanent magnet electric generator having an axially movable stator for adjusting the output voltage thereof. U.S. Pat. No. 3,443,135 (Lombard) discloses a permanent magnet variable voltage alternator having a two part, movable permanent magnet rotor. U.S. Pat. No. 3,360,667 (Gordon) discloses a generator having mechanically movable field magnets for changing the output voltage thereof. U.S. Pat. No. 3,713,015 (Frister) discloses an alternating current generator having a two part permanent magnet rotor which is adjustable in response to the output voltage thereof. U.S. Pat. No. 3,214,675 (Foster) discloses a permanent magnet generator having a supplemental rotary flux coil to regulate the output voltage thereof. U.S. Pat. No. 4,015,189 (Gordon) discloses a supplemental field excitation apparatus for the permanent magnet rotor of a pilot exciter to control the load regulation of a generator field winding.
U.S. Pat. No. 2,648,044 (Opel) discloses a voltage regulated generator having a control winding which utilizes the saturation region of operation to effect voltage regulation. U.S. Pat. No. 3,160,772 (Miron) discloses a plural voltage alternator having dual alternating current windings in a single field electromagnet. U.S. Pat. No. 3,551,784 (Shaw) discloses an alternating current generator having plural output windings for generating alternating current outputs which are electrically isolated from one another.
The following U.S. Pat. Nos. are also of interest: 3,237,034 (Krasnow) and 3,242,365 (Kaober).